The aviation industry is already working close to leak efficiency current planes use 20-30% less fuel than those produced 20 years ago. When Boeing developed the 787, they asked whether the industry wanted a supersonic plane or one with more efficiency. Industry chose more efficiency. Airbus responded with the A350.

The point is airlines are always trying to reduce fuel costs and planes are probably as efficient as they can be without the meddling of a dopey government bureaucracy.